An LTE network consists of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) Evolved NodeB (eNB) and an Evolved Packet Core (EPC), so as to realize the flatting of network. The EUTRAN includes a set of eNBs which are connected with the EPC through an S1 interface; the eNBs are connected to each other through X2 interfaces; and the S1 interface and the X2 interface are both logical interfaces. An EPC can manage one or more eNBs, one eNB can also be controlled by multiple EPCs, and one eNB can manage one or more cells.
An Self-organized Network (SON) is a technology that automatically configures and optimizes a network. The SON technology is featured by self-organization and self-optimization; the application of the SON technology in the LTE enables an eNB to automatically configure a network parameter according to a certain measurement and perform automatic optimization according to a network change, thereby keeping the performance of network optimum, and saving a lot of manpower and resources.
For the self-optimization of a handover parameter of the LTE system, it is needed to optimize cell selection and a handover-related parameter by a certain algorithm, according to the network operation state and the handover-related measurement, so as to improve the network performance. The above-mentioned handover is a handover in the LTE system or among systems, wherein the handover among systems is a handover to a Universal Terrestrial Radio Access Network (UTRAN) or a Global System for Mobile Communication (GSM) or a Code Division Multiple Access (CDMA) system. A process that UE performs a handover in a network is that: a network side makes a handover decision based on a handover algorithm and according to the signal quality of a local cell where the UE is and that of a neighboring cell which are reported by the UE, and then notifies the UE to execute a specific handover. A ping-pong handover, handover failure or Radio Link Failure (RLF), all of which are not expected, may be caused by improper handover parameter setting, have a negative impact on user experience and waste network resources. Therefore, for the self-optimization of a handover parameter, an accurate judgment on handover failure or undesirable handover scenario is the basis of an adjustment to the handover parameter.
The RLF happens to UE when the radio link signal quality is very bad or a handover is failed, and the UE performs Radio Resource Control (RRC) re-setup. When the UE performs the RRC re-setup, a target cell is obtained through cell selection. when the handover failure happens in the handover process, a source base station or a target base station retains information of a user, for the RRC re-setup. The UE includes a User Equipment Identity (UE-Identity) in an RRC re-setup request message, including a Cell Radio Network Temporary Identifier (C-RNTI) of the UE in a cell, short Medium Access Control integrity protection (short MAC-I) and a Physical Cell Identity (PCI). Wherein the C-RNTI is allocated in a source cell (aiming at a handover failure scenario), or allocated in a cell triggering the RRC re-setup (aiming at other scenarios except the handover failure scenario); the PCI is the physical address of the source cell (aiming at the handover failure scenario), or the physical address of the cell triggering the RRC re-setup (aiming at other scenarios except the handover failure scenario); and the short MAC-I is calculated by adopting the KRRCint key of the source cell (aiming at the handover failure scenario) or of the cell triggering the RRC re-setup and an integrity protection algorithm, and what is input is the PCI, the C-RNTI and an Evolved Cell Global Identifier (ECGI), wherein the PCI and the C-RNTI are included in an RRC re-setup message, and the ECGI is the one of the target cell selected by the UE during RRC re-setup.
As shown in FIG. 1, a too late handover scenario may be: RLF happens to UE in Cell b of eNB B, or the UE has failure in a handover from Cell b to Cell a, and then the UE attempts RRC re-setup in the Cell a of eNB A; what is said above shows that the UE performs a too late handover from the Cell b to the Cell a.
As shown in FIG. 2, a judgment on a too early handover scenario may be: RLF happens to UE in the Cell b soon after the UE performs a handover from Cell a of eNB A to Cell b of eNB B, or the UE has failure in a handover from the Cell a to the Cell b, and then the UE selects to perform RRC re-setup in the Cell a, namely, it returns back to the cell where the UE resides before the handover to perform the RRC re-setup; what is said above shows that the UE performs a too early handover from the Cell a to the Cell b.
As shown in FIG. 3, a scenario of a handover to a wrong cell may be: RLF happens soon after UE performs a handover from Cell c of eNB C to Cell b of eNB B, or the UE has failure in a handover from the Cell c to the Cell b, and then the UE performs RRC re-setup in the Cell a of the eNB A; what is said above shows that the selected Cell b of the eNB B is a wrong target cell, and the right target cell is the Cell a, namely, the UE should directly perform a handover from the Cell c to the Cell a.
During an RRC re-setup process, when the target eNB selected for re-setup does not have UE context, the RRC re-setup process would be failed, and the UE turns to an idle state. As shown in FIG. 4, RLF happens in Cell 2, UE initiates RRC re-setup attempt in Cell 1 and turns to an idle state after the RRC re-setup attempt is failed; the UE selects Cell 3 and performs RRC setup successfully. Thus the UE can enable an RRC setup complete message transmitted in the Cell 3 to include the contents of PCI, C-RNTI and short MAC-I which are formed during the first RRC re-setup, and the PCI of the target Cell 1 of the RRC re-setup attempt, and further include an indication of RLF-related measurement information. The RLF-related measurement information is the measurement results of signal quality of a serving cell and the best neighboring cell before the happening of RLF, wherein the measurement results are recorded by the UE; the measurement information can also include the measurement results of signal quality of a serving cell and the best neighboring cell, which are measured by the UE when initiating re-setup subsequently, or can also include position information of the UE.
As shown in FIG. 4, a method 1 of a handover scenario judgment is that: after receiving an RRC re-setup request message from the UE, base station 1 sends an RLF indication message to base station 2, and then the base station 2 judges whether it is a too early handover, a too late handover or a handover to a wrong cell according to the RLF indication message; after receiving an RRC setup complete message from the UE, the base station 3 initiates a request for obtaining RLF-related measurement information to the UE according to an indication of RLF-related measurement information, and the UE reports the RLF-related measurement information; the base station 3 sends obtained RLF-related measurement information and UE identity information to the base station 1, then the base station 1 sends the received information as the second part of the RLF indication message to the base station 2, and the base station 2 judges whether it is a covering problem according to the RLF-related measurement information.
As shown in FIG. 5, a method 2 of a handover scenario judgment is that: the base station 3 directly sends the obtained RLF-related measurement information and the UE identity information, which include the time difference between the last handover and the first RRC re-setup attempt, to the base station 2, then the base station 2 judges whether it is a handover problem or a covering problem; when it is the former, a specific handover scenario judgment is made, such as a too late handover, a too early handover and a handover to a wrong cell, according to the time difference between the last handover and the first RRC re-setup attempt.
In the judgment method 1 above, the base station 3 sends the RLF indication message only according to the PCI information of the Cell 1 in the RRC setup complete message, and the RLF indication message may be transmitted to a wrong eNB due to PCI aliasing. In the judgment method 2 above, due to the PCI aliasing, the base station 2 may map a wrong cell according to the PCI information of the Cell 1. To sum up, in the related art, a judgment is performed based on PCI, the PCI of a target cell is an identity of a physical layer, and different target cells are usually allocated with the same PCI when neighboring cell information of UE is allocated, thus causing PCI aliasing of target cells, thereby being incapable of uniquely determining the right target cell, and resulting in a high error rate of a handover scenario judgment.